Normal haemeostasis is the result of a complex balance between the processes of clot initiation, formation and dissolution. The complex interactions between blood cells, specific plasma proteins and the vascular surface, maintain the fluidity of blood, however in the case of injury, blood coagulation is vital for the containment of bodily fluids and is an important component of host defense mechanisms. Many significant disease states are related to abnormal clot formation (thrombosis) in blood vessels. For example, in arterial vasculature abnormal thrombus formation due to deterioration of an established atherosclerotic plaque is a major cause of acute myocardial infarction and unstable angina. In venous vasculature, many patients undergoing surgery, particularly in the abdominal and lower body regions, experience thrombus formation which reduces blood flow and can lead to a pulmonary embolism. Disseminated intravascular coagulopathy in both the venous and arterial systems occurs commonly during septic shock, some viral infections and cancer which often leads to rapid and widespread thrombus formation and organ failure.
Coagulation and clotting (thrombus formation) involves the sequential activation of multiple zymogens in a process leading to thrombin generation which in turn is responsible for the conversion of fibrinogen to an impermeable cross-linked fibrin clot. Thrombin production is the result of a blood coagulation cascade which has been intensively studied and increasingly characterized. See for example, Lawson, J. H., et al. (1994) J. Biol. Chem. 269:23357. The coagulation reactions of this cascade involve initiation, amplification and propagation phases. Additionally, the cascade has been divided into extrinsic and intrinsic pathways. The intrinsic pathway involves factors XII, XI, and IX and leads to the formation of a complex of factor IXa with its cofactor, factor VIIIa. This complex converts factor X to Xa. Factor Xa is an enzyme which forms a complex with its cofactor, factor Va, and rapidly converts prothrombin to thrombin. Thrombin in turn converts fibrinogen to fibrin monomers which polymerize to form a clot. The extrinsic pathway involves factor VIIa and tissue factor, which form a complex (TF/factor VIIa), and convert factor X to Xa. As in the intrinsic pathway, factor Xa converts prothrombin to thrombin.
Thrombin (factor IIa), as noted above, occupies a central position in the coagulation cascade by converting fibrinogen to fibrin. Consequently, substantial synthetic efforts have been directed to the development of compounds that bind to thrombin in order to inhibit its activity such as N-arylsulfinated phenylalanine amides. Additional compounds which have been prepared as synthetic thrombin inhibitors are disclosed in U.S. Pat. Nos. 5,656,600; 5,656,645; 5,670,479; 5,646,165; 5,658,939; 5,658,930 and WO 97/30073. Many thrombin inhibitors have been designed to mimic the structure of hirudin, a protein produced by medicinal leeches (Hirudo medicinalis), which binds to thrombin thereby inhibiting coagulation. Stubbs and Bode, Current Opinion in Structural Biology 1994, 4:823-832. Further synthetic thrombin inhibitors are reported in Annual Reports in Medicinal Chemistry, 1995-1997, Academic Press, San Diego, Calif.
TF/factor VIIa is a serine protease complex that participates in blood coagulation by activating factor X and/or factor IX. Factor VIIa is produced from its precursor, factor VII, which is synthesized in the liver and secreted into the blood where it circulates as a single chain glycopeptide. The cDNA sequence for factor VII has been characterized (Hagen et al., 1986, Proc. Natl. Acad. Sci. U.S.A., 83:2412-2416). A variety of natural and synthetic inhibitors of TF/factor VIIa are known and have varying potency and selectivity such as those disclosed in U.S. Pat. No. 5,589,173 used to treat myocardial infarction. Tissue factor pathway inhibitor (TFPI; Broze, 1995, Thromb. Haemostas., 74:90) and nematode anticoagulant peptide c2 (NAPc2; Stanssens et al., 1996, Proc. Natl. Acad. Sci. U.S.A., 93:2149) bind factor Xa prior to the formation of a quaternary inhibitory complex with the TF/factor VIIa complex. Small protein direct inhibitors (Dennis et al, 1994, J. Biol. Chem., 35:22137) and inactive forms of TF/factor VIIa are also known (Kirchhofer et al, 1995, Arteriosclerosis, Thrombosis and Vascular Biol., 15:1098; Jang et al, 1995, Circulation, 92:3041). Additionally, synthetic peptides and soluble forms of mutant TF which retain binding affinity but have reduced cofactor activity have been prepared (Roenning et al, 1996, Thromb. Res., 82:73; Kelley et al, 1997, Blood, 89:3219). U.S. Pat. No. 5,679,639 describes polypeptides and antibodies which inhibit serine protease activity. U.S. Pat. No. 5,580,560 describes a mutant factor VIIa which has an improved half-life. U.S. Pat. Nos. 5,504,067 and 5,504,064 describe a truncated TF for the treatment of bleeding. Kunitz domain-tissue factor fusion proteins have also been shown to be bifunctional anticoagulants (Lee et al, 1997, Biochemistry, 36:5607-5611). The TF/factor VIIa complex has been indicated as an attractive target for the development of inhibitors based on a dissociation between surgical bleeding and prevention of intravascular thrombosis (Harker et al, 1995, Thromb. Haemostas., 74:464).
Factor Xa is also central to thrombosis since it is a product of both the intrinsic and extrinsic coagulation pathways. Inhibitors of factor Xa have been synthesized such as bisamidine compounds (Katakura, S. (1993) Biochem. Biophys. Res. Commun., 197:965), compounds based on the structure of arginine (WO 93/15756; WO 94/13693) and phenyl and naphthylsulfonamides (WO 96/10022; WO 96/16940; WO 96/40679).
Percutaneous transluminal coronary angioplasty (PTCA) and recanalization are favored procedures for treating occluded vessels. However, arterial thrombosis following these procedures remains a leading cause of failure. Anticoagulants including heparin, the most widely used anticoagulant, have not been shown to be entirely effective or safe in the treatment and prevention of acute arterial thrombosis or rethrombosis. Accordingly, there remains a need for compounds which are effective inhibitors of enzymes in the coagulation cascade and which exhibit improved inhibitory activity and/or selectivity towards selected enzymes in the cascade.